Vector magnitude using orthogonal ECG leads during ventricular fibrillation is associated with defibrillation outcome.
Random fluctuations of ventricular fibrillation (VF) affect defibrillation; in addition, the heart is more susceptible to defibrillation at a higher absolute VF voltage (AVFV). Shocks delivered at higher AVFV waveforms from a single lead of the electrocardiogram (ECG) are more effective than conventional shocks. The authors investigated a new sensing method using multiple leads for better representation of the depolarization state of the heart. In this non-thoracotomy defibrillation study, a vector waveform derived from three orthogonal surface leads X, Y, and Z was analyzed in real time using two distinct defibrillation lead configurations, P1: RV-coil electrode (-) <--> (SVC-coil electrode + SCP) (+); and P2: RV-coil electrode (+) <--> (SVC-coil electrode + SCP) (-), where (-) represents cathode and (+) anode for the first phase of biphasic shock (RV = right ventricle, SVC = superior vena cava, SCP = subcutaneous patch). A PC-based closed-loop waveform-processing system, the peak-shock method (PSM), was developed to analyze the vector waveforms and trigger a biphasic shock at an AVFV peak. In using this defibrillation technique, an empirical threshold was applied to a weight function consisting of short-term and long-term moving averages of the vector VF waveform. A total of 340 shock trials in nine canine studies resulted in a significantly higher defibrillation success rate for the PSM compared with the conventional random-shock method (RSM), which involved shocking after a fixed VF time (54% for the PSM versus 42% for the RSM, p < 0.03). This further confirms that a susceptible period for defibrillation occurs during VF. The hardware/software design satisfied the requirements for processing the VF vector waveform in real time, and with the help of signal-processing techniques the high VF voltage could be detected at it occurred in real time. In addition, the P2 defibrillation lead configuration was significantly better than the P1 (p < 0.006).
Gurunathan
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Department of Biomedical Engineering, Medical College of Virginia, Richmond, USA.
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Lawton
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D000465:Algorithms; D000704:Analysis of Variance; D000818:Animals; D016009:Chi-Square Distribution; D017147:Defibrillators, Implantable; D004285:Dogs; D004553:Electric Conductivity; D004554:Electric Countershock / Q000295:instrumentation; D004562:Electrocardiography / Q000295:instrumentation; D004566:Electrodes; D004867:Equipment Design; D005260:Female; D008297:Male; D008955:Models, Cardiovascular; D012815:Signal Processing, Computer-Assisted; D016896:Treatment Outcome; D014693:Ventricular Fibrillation / Q000175:diagnosis* / Q000628:therapy